In a system including volatile memory, a battery backed memory may be available for preserving data in the event of a power failure. Low power condition is reliably sensed sufficiently in advance of supply voltage falling below a minimum operating voltage range so as to give an adequate time interval, e.g. 2.5 milliseconds for the saving of application operating system status. By using a voltage regulator signal which switches in a particularly sensitive manner toward a saturation or zero state well outside its normal control range to trigger a low power signal, such low power signal may provide a time interval of, e.g. from three to six milliseconds of advance warning of impending supply voltage failure. The system is particularly useful for hand-held data processing systems with rechargeable batteries since the regulator may provide its regulator signal as a common control signal for regulating multiple supply paths, and may only trigger the low power signal when all of such supply paths approach a failure condition.